As a sentinel disease for the diagnosis of AIDS, early reports of tuberculosis complicating AIDS seemed to indicate the disease was a result of reactivation of a previous infection, however today the picture of tuberculosis as a complication of AIDS has changed dramatically. The development of multidrug resistant strains of M. tuberculosis and the prospect of nosocomial transmission make the development of new, better tolerated therapies ever more important. It is the inclusion of pyrazinamide (PZA), an agent with a unique sterilizing activity, with isoniazid and rifampin (RIF) in current treatment regimens that constitutes the basis for 6-month short course therapy for M. tuberculosis (Mtb).l Surprisingly for a clinical agent, a detailed understanding of the mechanism of action of PZA continues to elude researchers. Recently the surprising observation was made that an analog of PZA, 5-chloropyrazinamide (5-CI-PZA), inhibits fatty acid synthetase I, (FAS 1) in Mycobacterium tuberculosis. This observation has been confirmed independently in other laboratories. In prokaryotes, the synthetase is typically composed of at least seven peptides that represent the individual enzyme components and are generally classified as Type II synthases. However in mammals and mycobacteria, the synthase activity is carried out by single high-molecular weight, multifunctional peptide chains which are known as Type I synthases. In cell free extracts of Saccharomyces cerevisiae not only was the activity of 5-CI PZA confirmed to be very comparable with that of the well-known inhibitor cerulenin in blocking the activity of FAS 1 it was also found that other pyrazinamide analogs also apparently inhibit FAS 1. The hypotheses to be tested in this proposal are that characterization of the mechanism of 5-CI-PZA on the inhibition of FAS 1 can lead to the development of better anti-mycobacterial agents and, secondly, that this inhibition process will be sensitive to structural variations of the pyrazinoic or nicotinic acid structure. The utility of the observed anti FAS activity can be enhanced by developing an understanding of the nature of the FAS 1 inhibition process so that this activity can be employed in the design of novel anti-tuberculous agents. As it is known that treatment of microbes with type I FAS inhibitors increases the sensitivity of those microbes to downstream inhibitors in a synergetic fashion, the development of anti-mycobacterial agents that act on FAS 1 and that can be used in combination with the aforementioned downstream agents may have a profound effect on improving tuberculosis treatment.